In Zwieg et al., U.S. Pat. No. 5,992,602, coins were discriminated by using an inductive sensor to take three readings as each coin passed through a coin detection station and these readings were compared against prior calibrated limits for the respective denominations. If a coin did not fall within certain specifications it was offsorted.
The optical sensing of coins in coin handling equipment has been known since Zimmermann, U.S. Pat. No. 4,088,144 and Meyer, U.S. Pat. No. 4,249,648. Zimmermann discloses a linear rail sorter with a row of photocells disposed across a coin track. Zimmermann does not disclose repeated measurements of a coin dimension as it passes the array, but suggests that there may have been a single detection of the largest dimension of the coin based on the number of photocells covered by a coin as it passes. Zimmermann does not disclose the details of processing any coin sensor signals derived from its photosensor.
Meyer, U.S. Pat. No. 4,249,648, discloses optical imaging of coins in a bus token collection box in which repeated scanning of chord length of a coin is performed by a 256-element linear light sensing array. Light is emitted through light transmissive walls of a coin chute and received on the other side of the coin chute by the light sensing array. The largest chord length is compared with stored acceptable values in determining whether to accept or reject the coin.
Brandle et al., U.S. Pat. No. 6,729,461, assigned to the assignee herein, disclosed a sensor with both optical and inductive sensors at a coin station within a coin sorting apparatus. Although the hybrid sensor was satisfactory for coin discrimination, it had certain drawbacks. It could not discriminate all of the coins in the Euro coin set, nor could it provide a counting accuracy to an error level of no more than 1:10,000, which is required for coin valuation. Another drawback was that coin dust tended to build up on a sapphire window portion of the optical sensor, thereby interfering with operation of the optical sensor. Still another drawback was manufacturing cost.
Therefore, a new coin counting/discrimination sensor is needed to overcome these limitations.